A conventional vehicle includes an occupant protecting system. The occupant protecting system includes a collision sensing device, which senses a vehicle collision, and an occupant protecting device, which protects the occupant in a cabin at the time of the vehicle collision. A known occupant protecting device includes a so-called airbag that deploys at collision. For example, Patent Literature 1 discloses a collision sensing device that detects air pressure of a space in a side door using an air pressure sensor. In the case where the collision sensing device detects sudden rise of the air pressure, the collision sensing device determines a side collision and deploys an airbag. A technique disclosed in Patent Literature 2 includes an air tank and a pressure sensor, which detects an internal pressure of the air tank, in a vehicle door. While a rising speed of the internal pressure is approximately proportional to a crushing speed of a vehicle-door outer panel, the maximum value of the internal pressure is approximately proportional to an amount of crush of the vehicle-door outer panel. In view of this, the technique measures a temporal change of an output signal from the pressure sensor so as to detect the rising speed of the internal pressure and the maximum value of the internal pressure. The technique consequently deploys an airbag when the rising speed and the maximum value exceed the respective threshold values.
A technique disclosed in Patent Literature 3 calculates a mass of a collision object based on a pressure on a bumper and a vehicle speed. Then, the technique corrects the mass based on the pressure and a temporal change of the pressure. The technique in turn determines whether or not the collision object is a pedestrian based on the corrected mass.